Low Complexity Precoding and Detection in Multi-User Massive MIMO OTFS Downlink

We consider the problem of degradation in performance multi-carrier multi-user massive MIMO systems when channel induced Doppler spread is high. Recently, Orthogonal Time Frequency Space (OTFS) modulation has been shown to be robust spread. In OTFS based systems, information symbols are embedded delay-Doppler (DD) domain where they jointly modulated generate time-domain transmit signal. Due multi-path delay and shifts, DD need demodulated at receiver. For communication (e.g., Division Multiplexing (OFDM)), have achieve high spectral energy efficiency with low complexity precoding downlink. Extending same downlink challenging due requirement for joint demodulation all user terminal (UT). this paper, we solve by proposing a novel precoder base station (BS) corresponding detector (LCD) terminals (UTs), which allows separate each symbol UT. The proposed increases only linearly increasing number BS antennas Q UTs. show, through analysis, that as (with total transmitted power decreased Q), achieves sum close achieved optimal Numerical simulations confirm our analysis also show error rate LCD UT) significantly more compared OFDM systems.